There areseveral important pieces of evidence that support the Big Bang theory. Amongthem, the two most prominent are Big Bang nucleosynthesis (BBN), a processresponsible for the creation of almost all the hydrogen we see in the universetoday, and the cosmic microwave background (CMB), which is electromagnetic radiationleft over from the formation of the universe. Prior to being observed, the cosmicmicrowave background was first predicted in connection with the work of RalphApherin, George Gamow, and Robert Herman on BNN in 1948. (NASA/WMAP Science Team, 2016) However,it wasn’t until many years later that sufficient technological advancements couldsearch for the evidence, and verify these hypotheses.Big Bang, orprimordial nucleosynthesis, is believed to have taken place from approximately10 seconds to 20 minutes after the Big Bang. (“Primordial Nucleosynthesis,”n.d.) The universe was hotter than the centre of a star, and nuclear fusionallowed the nuclei of “light elements” to form from protons and neutrons, despiteit being too hot for electrons to join these nuclei.
These ions would laterform neutral atoms when the universe had cooled sufficiently as a result ofexpansion. The Big Bang theory predicts the exact proportions of “light elements”like hydrogen, helium, lithium, and deuterium that would have been created as aresult of these specific conditions. (Jenks, 2014, 0:55)Thecurrent elemental composition of the universe is identifiable using theelectromagnetic spectrum. Each element has its own unique spectral signature,which can be used to identify the nature of stars, as well as other celestialbodies, and in turn what the universe is made of. Technology like the HubbleSpace Telescope allowed astronomers to see light from distance stars that wouldotherwise have been blocked by Earth’s atmosphere. Using Hubble’s Wide FieldCamera 3 and spectral emission data, scientists were able to identify thepercentage of elements that are abundant in today’s universe. (May, 2017) Itwas found that the universe is made of approximately 75% hydrogen and 25%helium, and the remaining elements make up less than 1%.
In addition, tests atlaboratories and particle research facilities have recreated the environmentsand energy levels present at the time of nucleosynthesis in order to determinewhether these elements could have been formed under these conditions. (O’Dowd, 2016, 7:20)Comparing the predictions from Big Bang theory with the data gathered byastronomers and astrophysicists, the accuracy to which the theory predicts thepercentages of each element is incredible. It is in direct agreement with thecomposition proposed in the Big Bang theory.The cosmicmicrowave background is thought to have been created 400,000 years after theBig Bang (and subsequently BBN) first took place. At this time the universe wasstill extremely hot and dense. These conditions made it impossible for atoms toform, and instead free electrons, and nuclei made of protons and neutrons, werescattered throughout the relatively small universe. This created an opaque plasmain which photons were unable to travel freely, as they would bounce off freeelectrons and remain trapped.
The CMB was created in a period of time known asthe Recombination Era, when the universe had cooled to a sufficient temperatureof approximately 3000K, and elements were then able to form. Subatomicparticles fused to form the element hydrogen, and because there were no longerfree electrons floating through space, the photons were able to escape. Thissurface, where the universe transitioned from opaque to transparent, is know asthe surface of last scattering. (Tate, 2013) These photons have been travellingthrough the universe ever since. Having been stretched out to infrared waves andthen eventually microwaves as a result of travelling through expanding space,they give us an image of what our universe looked like at 400,000 years old.
TheBig Bang theory predicts that the currently observable microwave backgroundradiation should have cooled to a temperature of about 2.7 degrees kelvin. (O’Dowd, 2016, 4:13)Evidence forCMB radiation was first accidentally discovered by Arno Penzias and RobertWilson in 1965 while the two were working at Bell Telephone laboratories inMurray Hill, New Jersey. They had constructed and were using a radiometer forexperiments involving satellite communications and radio astronomy.
However,they soon noticed their antenna picking up a background noise of about 2.7degrees above absolute zero in every direction that neither Penzias or Wilsoncould account for. (NASA/WMAPScience Team, 2016) They began troubleshooting to find the source, rulingout both urban and military radio interference, and even going as far as toremove pigeons who had been nesting in the radio antenna.
It was around thistime that the two heard about the work of physicist Robert Dicke at PrincetonUniversity. His research suggested that there should be a residual radiationthroughout the universe left over from the Big Bang, and he was planning ontesting his hypothesis. Both groups independently published their findings in ascientific journal, and in 1978 Penzias and Wilson received the Nobel Prize inPhysics for the discovery of the CMB.
(Levine, 2009)Muchlater, in the 1990’s the COBE (Cosmic Background Explorer) satellite waslaunched in order to attain a higher resolution microwave image of the CMB, andwas able to do so with an accuracy of 0.005% over the entire visible sky. Thisled to the important discovery that the radiation is uniform throughout theuniverse, with very little deviation in temperature.
These slight deviations arebelieved to have caused galaxies to form. (COBE, 2015)Scientistsstudying Big Bang theory continue to gather data and perform experiments astechnology becomes more powerful, but the major milestones in the discovery of evidenceto support Big Bang nucleosynthesis and the cosmic microwave background cannotbe overstated.